This invention relates generally to apparatuses and methods for injecting fluids and more specifically to an injector and associated method for injecting combustion fluids into a combustion chamber.
The combustion of carbon-based compounds, or carbonaceous fuels, is widely used for generating kinetic and electrical power. In one typical electric generation system, a carbonaceous fuel such as natural gas is mixed with an oxidizer and combusted in a combustion device called a gas generator. The resulting combusted gas is discharged to, and used to rotate, a turbine, which is mechanically coupled to an electric generator. The combusted gas is then discharged to one or more additional combustion devices, called reheaters, where the combusted gas is mixed with additional fuel and/or oxidizer for subsequent combustion. The reheaters, which typically generate pressures lower than those found in the gas generator, discharge the reheated gas to one or more turbines, which are also coupled to the electric generator.
The combustion in the gas generator and reheaters results in high temperatures and pressures. In some low-emission systems, pure oxygen is used as the oxidizer to eliminate the production of nitric oxides (NOx) and sulfur oxides (SOx) that typically result from combustion with air. Combustion of carbonaceous gases with pure oxygen can generate combustion temperatures in excess of 5000xc2x0 F. Such extreme conditions increase the stress on components in and around the combustion chambers, such as turbine blades and injectors. The stress increases the likelihood of failure and decreases the useful life of such components.
Injectors are used to inject the combustion components of fuel and oxidizer into the gas generator and the combusted gas, fuel, and/or oxidizer into the reheaters. Because of their position proximate to the combustion chamber, the injectors are subjected to the extreme temperatures of the combustion chamber. The injectors may also be heated by the passage of preheated combustion components therethrough. Failure of the injectors due to the resulting thermal stress caused by overheating increases operating costs, increases the likelihood of machine downtime, and presents an increased danger of worker injury and equipment damage.
One proposed injector design incorporates a mixer for combining a coolant with the fuel before the fuel is combusted. For example, U.S. Pat. No. 6,206,684 to Mueggenburg describes an injector assembly 10 that includes two mixers 30, 80. The first mixer 30 mixes an oxidizer with a fuel, and the second mixer 80 mixes coolant water with the prior mixed fuel and oxidizer. The mixture then flows through a face 121 to a combustion chamber 12 for combustion. The coolant water reduces the temperature of combustion of the fuel and, thus, the stress on system components. One danger presented by such a design is the possibility of xe2x80x9cflash back,xe2x80x9d or the combustion flame advancing from the combustion chamber into the injector. Flash back is unlikely in an injector outlet that has a diameter smaller than the mixture""s xe2x80x9cquenching distance.xe2x80x9d Thus, flash back can be prevented by limiting the size of the injectors. Undesirably, however, a greater number of small injectors is required to maintain a specified flow rate of the combustion mixture. The increased number of injectors complicates the assembly. Small injectors are also typically less space-efficient because the small injectors require more space on the face than would a lesser number of large injectors that achieve the same flow rate. Space on the face is limited, so devoting more space to the injectors leaves less space for other uses, such as for mounting other components. The small injectors are also subject to further complications due to their size. For example, small passages and outlets in the injectors can become blocked by particulates present in the fuel, oxidizer, or coolant. Thus, the reactants must be carefully filtered before passing through the injector. Moreover, typical reheaters are not designed to accommodate liquids, so the coolant water cannot be used in them.
In another proposed oxygen-fed combustion cycle, the gas generator is eliminated and gaseous combustion components are provided for initial combustion in a gas turbine combustor. The gas turbine combustor, sometimes also called a reheater, is similar to the reheater of the conventional cycle described above in that all of the inputs are in gaseous form. Cooling is achieved by diluting the combustion components with recirculated flue gas comprising steam and carbon dioxide. The flue gas dilutes the oxygen content in the combustion device and thus the combustion temperature. One such cycle, described as xe2x80x9cCombined Cycle Fired with Oxygen,xe2x80x9d is discussed in xe2x80x9cNew Concepts for Natural Gas Fired Power Plants which Simplify the Recovery of Carbon Dioxide,xe2x80x9d by Bolland and Saether, Energy Conversion Management, Vol. 33, No. 5-8, pp. 467-475 (1992). Advantageously, this cycle effectively reduces combustion temperatures, and the elimination of the gas generator simplifies the system. No special turbines are required for receiving hot gases from a gas generator, and the gas turbine combustor can discharge to a turbine that is designed for use with a conventional reheater. However, the gas turbine combustor is incompatible with the injectors designed for conventional gas generators, which provide inadequate flow rates and do not provide recirculated gases to the combustion chamber. Further, injectors for gas generators are typically designed to operate at the higher operating pressures found in a gas generator and are inoperable or inefficient when used in a lower pressure gas turbine combustor or reheater. Nor is the gas turbine combustor compatible with injectors designed for conventional reheaters, because the gas turbine combustor requires a lower pressure drop across the injectors than that provided in conventional reheaters.
Moreover, as the availability and price of various combustion fuels change, it is sometimes desirable to change the type of combustion fuel that is used. However, because different combustion fuels have different characteristics, such as heating values, conventional injectors must be adjusted or replaced in order to provide efficient service with the different fuels. Thus, changing the type of fuel that is combusted in a system requires servicing the injectors and thereby interrupting service, reducing output, and increasing costs.
Thus, there exists a need for an apparatus and method for injecting fluid components of combustion into a combustion chamber of a combustion device. The apparatus and method should provide for injection of a recirculated gas to limit the temperature of the injector to decrease thermal stress, likelihood of failure, and operating costs. The injectors should be compatible with combustion devices that inject gaseous coolants, including reheaters, and should provide efficient injection and mixture of combustion gases of various types and heating values.
The present invention provides an injector and an associated method for injecting and mixing gases, comprising a carbonaceous fuel and oxygen, into a combustion chamber of a combustion device. The injector may have an annular space proximate to its perimeter, through which a recycled mixture of steam and carbon dioxide can be injected to limit the combustion temperature, thereby decreasing thermal stress on components in and around the combustion chamber. Further, the injector has different jets, which can be used to separately inject different combustion fuels. Thus, the same injector can permit different combustion fuels to be alternatingly injected, each under the proper conditions. The injector is compatible with combustion devices that inject only gaseous fluids, including a reheater. The injector can be used in a reheater that recombusts a combusted gas that is discharged from a gas generator and turbine. Alternatively, the injectors can be used in a reheater that is the initial combustion device in a power generation cycle.
According to one aspect of the present invention, there is provided an injector for injecting combustion fluids into a combustion chamber. The injector includes an injector body that defines an injector face facing the combustion chamber, a main bore, and at least one main jet extending from the injector face to the main bore. A first plurality of fuel jets extend from the injector face and are fluidly connected to a first fuel inlet, typically by means of a first fuel manifold. Similarly, a second plurality of fuel jets extend from the injector face and are fluidly connected to a second fuel inlet, typically by means of a second fuel manifold. The central axis of each of the fuel jets defines a converging angle relative to one of the main jets such that fluid flowing from the fuel manifolds into the combustion chamber through the fuel jets impinges on a stream of fluid flowing from the respective main jet. The converging angle may be between about 10xc2x0 and 45xc2x0 such that convergence occurs in the combustion chamber. According to other aspects of the invention, a center of each of the main jets is located at least about 4 inches from the centers of the other main jets, and each of the main jets has a diameter of at least about 1 inch.
The main bore may be fluidly connected to a source of oxidizing fluid substantially free of nitrogen and sulfur, the first fuel manifold may be fluidly connected to a first source of fuel, including hydrogen and carbon monoxide, and the second fuel manifold may be fluidly connected to a second source of fuel, including methane. Each of the first and second manifolds comprise an annular space that extends circumferentially around at least one of the main jets. In another embodiment, each of the second fuel jets may be smaller in cross sectional area than each of the first fuel jets. As such the fuel jets may be tailored to the delivery requirements necessary for the particular type of fuel to be injected via the fuel jets.
In one advantageous embodiment, the injector also includes a first sleeve that defines an interior space. The injector body is positioned in the interior space such that a first annular space is defined between the injector body and the first sleeve. In one aspect of the invention, the first annular space is fluidly connected to a source of a recycle gas comprising steam and carbon dioxide. In another aspect, the injector includes a recycle gas inlet and a second sleeve which defines a second annular space between the first and second sleeves. The first sleeve defines at least one first sleeve aperture fluidly connecting the first annular space to the second annular space, and the second sleeve defines at least one second sleeve aperture fluidly connecting the second annular space to the recycle gas inlet. In a further aspect, the injector includes a circumferential passage that extends along the perimeter of the second sleeve and fluidly connects the second annular space to the recycle gas inlet so that gas enters the recycle gas inlet and flows generally in a first direction in the second annular space and a second, generally opposite, direction in the first annular space. According to another aspect of the invention, the injector body also defines a coolant chamber that is configured to receive and circulate a coolant fluid.
The present invention also provides a method of injecting combustion fluids into a combustion chamber. At least one stream of oxidizing fluid, including oxygen and substantially free of nitrogen and sulfur, is injected into the combustion chamber. The oxidizing fluid may be injected in streams located with at least about 4 inches between their centers, and each stream may have a diameter of at least about 1 inch. A first combustion fuel and a second combustion fuel are alternatingly injected through fuel jets into the combustion chamber and impinged on the stream of oxidizing fluid. The fuel can be injected through a manifold defining an annular space that extends circumferentially around at least one of the main jets, and can be injected at a converging angle between about 10xc2x0 and 45xc2x0 relative to the stream of oxidizing fluid such that convergence occurs in the combustion chamber. The method also includes combusting the fuel with the oxygen. In one aspect of the present invention, a recycle gas including steam and carbon dioxide is injected into the combustion chamber through a first annular space at an inside perimeter of the combustion chamber, for example, to limit the combustion temperature to about 4000xc2x0 F. In another aspect, a coolant fluid is circulated through at least one coolant chamber in an injector body.
Thus, the present invention provides an injector and method for injecting combustion fluids, for example, into a gas generator or reheater, through a first and second plurality of fuel jets. Different combustion fluids can be injected through fuel jets and combusted efficiently, thereby increasing the versatility of the injector and decreasing the necessity of replacing or modifying the injector. Additionally, the injector and method limit the temperature of the injector and decrease the thermal stress on the components, thereby decreasing the likelihood of failure and the operating costs.